Many businesses, such as automobile repair shops, routinely encounter work pieces, such as bolts, nuts or the like, that are extremely difficult to remove or place. The difficulty can be a result of the work piece being fixed-in-place, as by rust or over tightening, or because the work piece is in a location that is difficult to reach. For example, a bolt may be underneath another part that blocks access to it or otherwise inhibits the swinging action of a handle of a tool, such as wrench, while engaging it and applying torque. This makes removal or installation of certain work pieces difficult and time consuming.
It is often necessary to remove blocking parts to gain access to the work piece of interest with a wrench, such as an open-end or a box-end wrench. There is a need for a wrench that can expeditiously reach and remove work pieces and not require surrounding space for manipulation of the lever-handle. There is also a need to apply sufficient torque without exhaustive human effort. One solution is a powered wrench, wherein torque is supplied to the work-piece-engaging part of the wrench by a motor.
Such a powered wrench would have a gearbox for transmitting the power. One requirement would be for the gearbox profile to be as small as possible to navigate tight spaces. Another requirement would be for the power to be transmitted through the handle; or, in other words, perpendicular to the axis of the work-piece-engaging part of the wrench. Both requirements are met by a worm gearbox.
In a worm gearbox, a screw transmits power to a spur gear. The axes of the screw, or worm, and the spur gear are perpendicular. Such an arrangement is typically smaller than other configurations having the same gearing ratio and involving multiple spur gears. Sometimes the gear train includes an intermediate, or idler, gear between the worm gear and the spur gear doing the work, or drive gear. This configuration allows different spatial arrangements of the gear system.
As known in the art, it takes a complete revolution of the worm gear to advance the drive gear one tooth. A 30-tooth drive gear, for example, would have a 30:1 reduction in speed and a complementary 30:1 increase in torque. It should be noted that the idler gear is inconsequential with respect to the gear ratio since it transmits motion but does not contribute any mechanical advantage. This low-speed-high-torque gearing arrangement is particularly well matched to motor drives, which drives characteristically produce high revolution speed with low torque.
Worm gear configurations for powered wrenches are known in the art. For example, in U.S. Pat. No. 6,543,313 to Samudosky et al, a prior patent of the instant inventor which is incorporated herein by reference, a worm gearing arrangement driving a chain sprocket is disclosed. The chain provides an adaptable means for engaging the work piece. The chain, however, is subject to breakage and, on occasion, slippage.
U.S. Pat. No. 858,892 to Moss teaches a worm gearing arrangement to drive a spur gear with a box recess to engage a nut. The box recess provides a firm and virtually unbreakable grip on the work piece. Adaptation to smaller work pieces is provided by inserts to the box recess similar to socket-wrench sockets. Moss uses an idler gear to make the layout compact for tight spaces. The drive force, however, is supplied by twisting the handle by hand and is not supplied by motor. This twisting can be fatiguing for the operator, particularly considering the slow speed of the operation.
Considering that higher torque is usually only needed in the initial loosening of a work piece, such as a nut, and that the subsequent unthreading of the nut following its loosening is characterized by lower frictional forces, it would be desirable to have a means to switch from high torque to lower torque, and, in doing so, to hasten the speed of the action. Furthermore, not all work pieces require the same initial “breaking” torque. However, a wrench designed to be powerful enough for the occasional “frozen” nut, will of necessity be slow in operation. What is needed in such cases is a dual-speed option.
U.S. Pat. No. 3,272,037 to Bruehl describes a wrench having dual speeds. The slow speed is provided in a manner similar to Moss above. The fast speed is provided by a ratchet mechanism enabling the handle to be used in the conventional way, that is, by swinging the handle by hand. This does not solve the problem for a restricted space, however, because there would be insufficient room to swing the handle.
What is missing in the prior art is a gear-driven motor-powered wrench for fitting into tight spaces with a changeable gear ratio providing both slow and fast speeds.